Variable Retention Harvest (Cutfoot​ ​Sioux​ ​Experimental​ ​Forest)

State or Province
Nearest city or town
Max, MN
Describe the location
Dry, Mesic Pine-Oak, Cutfoot Experimental Forest
Cutfoot Sioux Experimental Forest
Cover type
Forest health threats
Adaptive silviculture options
Silviculture system
Estimated year of stand origin
Additional information about stand origin
This is a natural fire origin red pine stand
Site preparation method
Soil texture
Soil details
(Itasca​ ​County)​ ​867B,​ ​Menahga​ ​and​ ​Graycalm​ ​soils
Stand area
15 acres
Treatment area
13 acres

47.55472, -94.093701


The​ ​purpose​ ​of​ ​this​ ​study​ ​is​ ​to​ ​demonstrate​ ​different​ ​retention​ ​patterns​ ​of​ ​red​ ​pine​ ​as​ ​stands approach​ ​old​ ​age.​ ​This​ ​study​ ​will​ ​demonstrate​ ​and​ ​test​ ​differing​ ​spatial​ ​patterns​ ​and​ ​densities​ ​in old​ ​age​ ​red​ ​pine​ ​stands​ ​as​ ​a​ ​means​ ​to​ ​promote​ ​multi-cohort,​ ​structurally​ ​and​ ​biologically complex​ ​stands​ ​that​ ​will​ ​produce​ ​both​ ​silvicultural​ ​and​ ​economic​ ​outcomes.​ ​Silvicultural​ ​and economic​ ​management​ ​outcomes​ ​include;​ ​quality​ ​production,​ ​quantity​ ​production,​ ​production​ ​of specific​ ​materials​ ​and​ ​sound​ ​ecological​ ​management​ ​for​ ​all​ ​products.​ ​This​ ​demonstration​ ​is unique​ ​because​ ​it​ ​has​ ​not​ ​been​ ​implemented​ ​at​ ​this​ ​age​ ​of​ ​stand​ ​in​ ​the​ ​lakes​ ​states​ ​region​ ​to​ ​our knowledge.​ ​

The​ ​stand​ ​will​ ​be​ ​commercially​ ​thinned​ ​to​ ​a residual stand​ ​average​ ​of​ ​60​ ​sq ft per acre ​using​ ​differing​ ​levels​ ​of​ ​retention distributed across the 15 acres.​ ​The​ ​demonstration​ ​area​ ​will​ ​contain​ ​three​ ​1/2-acre​ ​aggregates​ ​of​ ​unthinned​ ​forest, three​ ​1/4-​acre​ ​aggregates​ ​of​ ​unthinned​ ​forest,​ ​and​ ​the​ ​remainder​ ​of​ ​the​ ​stand​ ​will​ ​be​ ​thinned to​ ​a​ ​residual​ ​basal​ ​area​ ​of​ ​37.5​ ​sq​ ​ft​ ​per​ ​acre.​ ​No​ ​new​ ​roads​ ​or​ ​landings​ ​would​ ​be​ ​needed​ ​as​ ​this stand​ ​is​ ​bordered​ ​by​ ​forest​ ​road​ ​2171​ ​and​ ​access​ ​points​ ​are​ ​already established​ ​from​ ​adjoining​ ​​units.

The​ ​short-term​ ​goals​ ​are​ ​to​ ​increase​ ​species​ ​and​ ​structural​ ​diversity,​ ​and​ ​to​ ​create​ ​variation​ ​in canopy​ ​cover,​ ​tree​ ​density,​ ​and​ ​understory​ ​plant​ ​community​ ​development.​ ​The​ ​long-term​ ​goals are​ ​to​ ​increase​ ​stand​ ​heterogeneity​ ​and​ ​achieve​ ​structure​ ​associated​ ​with​ ​multi-cohort​ ​red​ ​pine stands,​ ​increase​ ​species​ ​diversity​ ​and​ ​stand​ ​structure,​ ​increase​ ​and​ ​maintain​ ​dead​ ​woody​ ​debris, minimize​ ​windthrow,​ ​increase​ ​growth​ ​of​ ​residuals,​ ​and​ ​retain​ ​large​ ​individuals.

Figure 1: CNF variable retention red pine treatment aerial image.

Silviculture Objective(s)

The​ ​prescription​ ​called​ ​for​ ​a​ ​commercial​ ​thin​ ​between​ ​December​ ​1,​ ​2010​ ​and​ ​May​ ​15,​ ​2011.

Short-term​: Thin​ ​to​ ​a​ ​stand-level​ ​average​ ​of​ ​60​ ​ft​2​/ac​ ​residual​ ​basal​ ​area​ ​using​ ​variable​ ​retention​ ​of​ ​unthinned reserve​ ​patches​ ​embedded​ ​within​ ​a​ ​thinned​ ​forest. 

The​ ​stand​ ​will​ ​remain​ ​a​ ​red​ ​pine​ ​community​ ​with​ ​short-term​ ​goals​ ​of​ ​increasing​ ​species​ ​and structural​ ​diversity.​ ​​This​ ​intermediate​ ​entry​ ​would​ ​provide​ ​improved​ ​growing​ ​conditions​ ​for dispersed​ ​residual​ ​trees​ ​while​ ​maintaining​ ​species​ ​and​ ​structural​ ​diversity​ ​for​ ​wildlife​ ​objectives within​ ​aggregate​ ​reserves.​ ​Create​ ​variation​ ​in​ ​canopy​ ​cover,​ ​tree​ ​density,​ ​and​ ​understory​ ​plant community​ ​development.​ ​Red​ ​pine​ ​would​ ​continue​ ​to​ ​be​ ​the​ ​primary​ ​overstory​ ​species,​ ​but​ ​other species​ ​components​ ​would​ ​be​ ​present​ ​(e.g.​ ​white​ ​pine,​ ​white​ ​spruce,​ ​paper​ ​birch)​ ​in​ ​higher percentages​ ​than​ ​pre-harvest​ ​conditions. 

Long-term​ ​(including​ ​future​ ​entry​ ​needs):​​ ​​ ​Increase​ ​stand​ ​heterogeneity​ ​and​ ​achieve​ ​structure associated​ ​with​ ​multi-cohort​ ​red​ ​pine​ ​stands.​ ​Goals​ ​include:​ ​increasing​ ​species​ ​diversity​ ​and stand​ ​structure;​ ​increase​ ​and​ ​maintain​ ​dead​ ​woody​ ​debris,​ ​minimize​ ​windthrow,​ ​increase​ ​growth of​ ​residuals,​ ​and​ ​retain​ ​large​ ​individuals.

Pre-treatment stand description and condition

Pre-treatment species composition: 

This​ ​stand​ ​is​ ​dominated​ ​by​ ​red​ ​pine​ ​in​ ​the​ ​overstory.​​​ Scattered​ ​overstory​ ​components​ ​include white​ ​pine,​ ​paper​ ​birch,​ ​balsam​ ​fir,​ ​and​ ​white​ ​spruce.​ ​Red​ ​maple,​ ​paper​ ​birch,​ ​white​ ​pine​ ​and white​ ​spruce​ ​seedlings​ ​and​ ​saplings​ ​are​ ​scattered​ ​in​ ​the​ ​understory.

Figure 2: A photo of the composition of the stand pre-harvest.

Pre-treatment forest health issues: 

Deer​ ​browse​ ​is​ ​a​ ​concern ​for​ ​regeneration.​ Some existing armillaria root rot pockets are present in the stand.

Landowner objectives/situation: 

This​ ​prescription​ ​is​ ​being​ ​conducted​ ​as​ ​an​ ​experiment​ ​to​ ​demonstrate​ ​different​ ​retention​ ​patterns of​ ​red​ ​pine​ ​as​ ​stands​ ​approach​ ​old​ ​age,​ ​and​ ​it​ ​will​ ​demonstrate​ ​and​ ​test​ ​differing​ ​spatial​ ​patterns and​ ​densities​ ​in​ ​old​ ​age​ ​red​ ​pine​ ​stands​ ​as​ ​a​ ​means​ ​to​ ​promote​ ​multi-cohort,​ ​structurally​ ​and biologically​ ​complex​ ​stands​ ​and​ ​will​ ​produce​ ​both​ ​silvicultural​ ​and​ ​economic​ ​outcomes.

Silviculture Prescription

Harvest Method:  Commercial thin

Season of Operation:  Winter harvest between December 1, 2010 and May 15, 2011;

Marking Guide and Mitigations:

  • Use​ ​a​ ​variable​ ​retention​ ​approach​ ​to​ ​thin​ ​stand​ ​to​ ​an​ ​average​ ​of​ ​60​ ​ft​2​/ac​ ​residual​ ​stand basal​ ​area.​ ​​​This​ ​prescriptions​ ​variable​ ​retention​ ​approach​ ​consists​ ​of​ ​unthinned​ ​reserve patches​ ​of​ ​two​ ​sizes​ ​(¼-​ ​and​ ​½-acre)​​​ ​and​ ​a​ ​thinned​ ​matrix.
  • Unthinned​ ​reserve​ ​patches:​ ​Leave​ ​15%​ ​of​ ​the​ ​stand​ ​in​ ​three​ ​¼-acre​ ​and​ ​three​ ​½-acre reserves​ ​patches​ ​to​ ​provide​ ​natural​ ​tree​ ​mortality​ ​and​ ​for​ ​wildlife​ ​objectives.
    • Reserve​ ​patches​ ​are​ ​uncut​ ​“Skips”​ ​that​ ​are​ ​identified​ ​by​ ​unique​ ​attributes​ ​to​ ​be reserved.
      • Large​ ​snags,​ ​unique​ ​species,​ ​structurally​ ​unique,​ ​large​ ​downed​ ​dead​ ​wood, unique​ ​understory​ ​species,​ ​or​ ​advanced​ ​regeneration.
    • Create​ ​circular​ ​patches​ ​with​ ​59​ ​and​ ​83​ ​foot​ ​radius,​ ​respectively,​ ​for​ ​¼-​ ​and​ ​½-acre reserve​ ​patches.
  • Thinned​ ​matrix:​ ​Between​ ​the​ ​reserve​ ​patches,​ ​thin​ ​to​ ​37.5​ ​ft​2​/ac​ ​residual​ ​stand​ ​basal​ ​area by​ ​dispersed​ ​free​ ​thinning​ ​to​ ​maximize​ ​species​ ​diversity​ ​and​ ​structural​ ​complexity. 
    • Mark​ ​reserve​ ​trees​ ​that​ ​are​ ​windfirm​ ​and​ ​in​ ​dominant​ ​canopy​ ​positions.
    • Maximize​ ​species​ ​diversity​ ​in​ ​reserve​ ​trees.
    • Thin​ ​primarily​ ​from​ ​below.
    • Cut​ ​primarily​ ​suppressed​ ​or​ ​codominant​ ​red​ ​pine​ ​and​ ​jack​ ​pine​ ​to​ ​maintain existing​ ​species​ ​diversity​ ​in​ ​the​ ​stand.​ ​​ ​Retain​ ​other​ ​species​ ​unless​ ​needed​ ​for operability.
  • ​Leave​ ​at​ ​least​ ​6-10​ ​standing​ ​dead,​ ​suppressed,​ ​or​ ​dying​ ​conifers​ ​per​ ​acre. Preference​ ​is​ ​given​ ​to​ ​short-lived​ ​species,​ ​such​ ​as​ ​jack​ ​pine.​ ​Other​ ​species​ ​include​ ​white spruce,​ ​balsam​ ​fir,​ ​red​ ​and​ ​white​ ​pine,​ ​black​ ​spruce​ ​and​ ​tamarack.​ ​​Trees​ ​may​ ​be scattered​ ​or​ ​clumped.​ ​Snags​ ​greater​ ​than​ ​12​ ​inches​ ​will​ ​be​ ​marked​ ​as​ ​reserve. Retain​ ​dying, ​damaged,​ ​and​ ​diseased​ ​pine​ ​for​ ​wildlife​ ​(e.g.,​ ​black-backed​ ​woodpecker). Retain​ ​existing​ ​snags​ ​greater​ ​than​ ​5​ ​inches​ ​unless​ ​a​ ​safety​ ​hazard.​ ​​
  • Protect​ ​conifer​ ​regeneration​ ​as​ ​possible​ ​throughout​ ​the​ ​site.
  • Lop​ ​and​ ​scatter​ ​slash​ ​within​ ​3’​ ​of​ ​ground​ ​throughout​ ​stand. 
  • Goshawk​ ​nest​ ​post-fledging​ ​area:​ ​maintain​ ​an​ ​average​ ​of​ ​70​ ​percent​ ​canopy​ ​cover​ ​across the​ ​250​ ​acre​ ​post-fledging​ ​area.

Figure 3:  Variable retention harvest

Post-harvest Treatment:

Site​ ​Preparation​:​ Implement​ ​mechanical​ ​reduction​ ​of​ ​shrub​ ​and​ ​slash after​ ​harvest​ ​on the thinned portion of the stand with the use of Chippewa harrow (disc's mounted on a skidder).

Figure 4: The structure of the stand upon completion of disking. 

Reforestation:​ Planting​ ​additional​ ​species​ ​after​ ​harvest and site preparation; planting would be conducted in the thinned portion of the stand at a density of 200 trees per acre each of white pine, jack pine, and white spruce.

Stand​ ​Protection: Bud capping as necessary to protect planted seedlings from deer browse annually for up to 5 years

Individual Tree Release: If necessary, release planted stock at year 4 post-planting to promote growth and survival of planted seedlings.

Post-treatment assessment

The average stems per acre five years after the treatment can be seen in Table 1. Figure 2 below further breaks down the stems per acre by species and site prep treatment for the pre-harvesting conditions as well as the post-harvesting conditions up to five years after the treatment.

Table 1. Average stems per acre five years post-treatment. 

90 135 562 517 4811 472 33477 14299


Figure 5: The stems per acre broken down by species and site prep treatment for the pre-harvesting conditions as well as the post-harvesting conditions up to five years after the treatment.

The Northern Research Station monitored planted stock survival on 30 seedlings of each species over five years following treatment. Table 2 shows survival of the three planted species based on planting location in a harrowed area vs. a non-harrowed area. Figure 3 (below) shows a more in-depth breakdown of the planted stock survival and the likely cause of death. Jack pine in particular was heavily browsed over the other two species.

Figure 6:  Planted stock survival by species and type of site preparation (harrow vs no action) five years after planting. Additional treatments included annual bud capping and individual tree release at year 4.

Table 2. Planted species survival based on site preparation treatments.

Species (treatment) Survival Mortality
Jack Pine (harrow) 53% 47%
Jack Pine (no site prep) 27% 74%
White Pine (harrow) 73% 27%
White Pine (no site prep) 73% 27%
White Spruce (harrow) 60% 40%
White Spruce (no site prep) 73% 27%

The Northern Research Station also followed planted stock growth on the same 30 trees of each species over five years.  Table 3 shows diameter and height growth of white pine to be significantly greater in the harrowed portion of the stand compared to the no prep. Jack pine and white spruce diameter and height growth vary between the harrow and no action treatment. 

Table 3. Diameter and height response of the three planted species five years post-planting based on site preparation.   

Species Harrow No Prep
5 Year Height    
Jack Pine 28.7 cm  29.6 cm 
White Pine 79.6 cm  48.8 cm 
White Spruce 61.6 cm  69.4 cm 
5 Year Diameter    
Jack Pine 3.7 mm 3.4 mm
White Pine 8.3 mm 5.5 mm
White Spruce 8.1 mm 10.0 mm

Figure 7: A post-harvest reserve is seen on the right.

Figure 8 : CNF variable retention red pine treatment during an April 2018 tour showing an unharvested patch at right.

Plans for future treatments

The Northern Research Station has scheduled vegetation monitoring of residual tree growth and survival (in research plots) every five years. Survival and growth of planted stock and all other woody species will be conducted annually for the first 5 years then periodically every 2-5 years thereafter.

No other future vegetation treatments are planned at this time but could be considered as vegetation monitoring continues.

Costs and economic considerations

This​ ​project​ ​was​ ​funded​ ​by​ the Northern Research Station and timber proceeds covered post-harvest treatments including; site prep, planted stock and planting, individual tree release, and bud-capping.

Other notes

This case study was developed with support from the United States Department of Agriculture's National Institute for Food and Agriculture (USDA-NIFA), Renewable Resources Extension Act (RREA). Project #MIN-44-E02, principal investigator Eli Sagor, University of Minnesota.

Summary / lessons learned / additional thoughts

Some things that were considered for future variable retention harvest for this forest type could be to plant ​​climate​ ​change​ ​adapted​ ​oak​ ​species​ ​such​ ​as​ ​bur​ ​oak​ ​or​ ​white​ ​oak​ ​to provide​ ​options​ ​for​ ​a​ ​higher​ ​commercial​ ​value​ ​product.​ ​It​ ​also​ ​could​ ​have​ ​been​ ​beneficial​ ​to​ ​vary the​ ​residuals​ ​in​ ​the​ ​matrix​ ​spatially​ ​to​ ​promote​ ​increased​ ​growth​ ​and​ ​survival​ ​of​ ​the​ ​intolerant species​ ​to​ ​favor​ ​jack​ ​pine​ ​and​ ​red​ ​pine.​ ​Summer harvest would have been preferred for increased scarification. Site prep was effective at reducing hazel and favored increased seedling growth for white pine. During individual tree release oak stump sprouts could have been reduced to one or two good form individuals to encourage good formed bole and increase growth. Overall,​ ​the​ ​goals​ ​to​ ​increase​ ​growth​ ​of​ ​residuals, promote​ ​multi-cohort​ ​development,​ ​reserve​ ​unique​ ​biological​ ​legacies,​ ​and​ ​create​ ​more​ ​complex structure​ ​were​ ​achieved.